With many services and applications provided in mobile radio systems, such as news groups, video conferences, video on demand, distributed applications, etc., it is necessary to transmit messages not just to one but to two or more mobile radio users.
In principle, it is possible to this end when transmitting messages to the different users to send each recipient a copy of the data. This method is simple to implement but requires a very high bandwidth, particularly for large groups, as the message is transmitted via a number N of individual connections (unicast connections) and is thereby sent a number of times via common connection paths, whereby N specifies the number of recipients of the message.
A so-called point-to-multipoint transmission (multicast transmission) is therefore deployed in modern mobile radio systems, characterized by the fact that different users, to whom the same message is to be transmitted, are combined in a group (multicast group), with one address (multicast address) being assigned to this group, so that data to be transmitted is sent only once to this multicast address and is ideally sent only once via common connection paths from the sender to the recipients. The sender does not have to know how many recipients are concealed behind the multicast address. In order to receive the messages of a specific multicast group, a user simply has to register with the multicast group.
Alternatively, a method referred to as broadcast also may be deployed, in which messages are sent to all users within a regional area, whereby this area, in which the broadcast messages are transmitted, is referred to as the broadcast area and the size of the broadcast area is determined by the network operator. Ideally, the message is thereby sent only once with this method as well. It is, however, a disadvantage here that with this method all users within the broadcast area are always able to read broadcast messages.
To understand the problems more easily, individual components of the architecture of a UMTS mobile radio network are examined in more detail below by way of an example; in particular, the different types of channel known from this context, which are used as the interface between different layers and protocols of the so-called protocol stack provided according to the OSI reference model.
FIG. 1 shows the interfaces between a data link layer LAYER2 provided according to the OSI reference model, including a protocol for medium access control MAC and a protocol to support segmentation and return for useful data and signaling data (radio link control) RLC, and the bit transmission layer (physical layer) LAYER1.
Data is transmitted on logical channels between RLC and LAC, whereupon in MAC the logical channels LogCH are mapped onto transport channels TrCH according to specific rules, whereby it is also possible for a number of logical channels LogCH to be mapped onto a transport channel TrCH by multiplexing.
Logical channels LogCH, which are mapped onto the same transport channel TrCH, have to satisfy identical or similar requirements with regard to transmission quality and quality of service (QoS).
Corresponding steps are therefore implemented for each transport channel TrCH in the bit transmission layer LAYER1, such as the appending of so-called CRC blocks, which can be used to identify transmission errors, and channel coding, which can be used to correct errors that occur.
When these steps have been implemented for each of the transport channels TrCH, specific transport channels TrCH are multiplexed on a so-called coded composite transport channel CCTrCH within the bit transmission layer LAYER1. This coded composite transport channel CCTrCH is then, in turn, mapped onto one or a number of physical channels PhyCH and transmitted via an air interface defined according to UMTS.
Data in the form of so-called transport blocks (TB) is transmitted on the transport channels TrCH. A number of TBs thereby may be transmitted at the same time within a specific time interval (Transmission Time Interval TTI) in the form of a so-called transport block set (TBS).
Parameters such as the size of a transport block, the number of transport blocks transmitted per transport block set, the duration of a time interval, like other parameters, are defined by a so-called transport format (TF). The set of all transport formats that can be used by a transport channel TrCH is, in turn, defined by a transport format set (TFS). A so-called transport format identifier (TFI) is defined to identify a specific transport format within a transport format set.
Transport blocks of different transport channels TrCH, which are mapped onto the same coded composite transport channel CCTrCH during a time interval, have to satisfy specific prerequisites; i.e., not every combination of transport blocks is permitted.
Permitted combinations of transport blocks of different transport channels TrCH, which can be mapped onto the same coded composite transport channel during a time interval, are defined by so-called transport format combinations (TFC). The set of all permitted transport format combinations is, in turn, defined by a so-called transport format combination set (TFCS).
A so-called transport format combination indicator (TFCI) is defined to identify certain transport format combinations within a transport format combination set. As such, the transport format combinations used, which can change from time interval to time interval, do not have to be defined specifically every time and transferred to a mobile radio device, but can be referred to by an indicator (the transport format combination indicator) on a list of transport format combinations in a very efficient manner.
A further increase in efficiency is achieved in that when the transport format combinations are being configured they are not transmitted specifically but a calculated transport format combination (CTFC) is calculated, from which the transport format identifier then may be calculated back in the mobile radio device, indicating the corresponding TFs within the transport format sets of the individual transport channels TrCH and the required transport format combination, in turn, results.
So that a mobile radio device can forward data, which it receives via its physical channels, via transport channels TrCH to higher protocol layers, it has to know the transport formats of the individual transport channels TrCH. If a number of transport channels TrCH is mapped onto a coded composite transport channel, it must know the transport formats of each individual transport channel TrCH, in order to allocate the data packets with different characteristics (according to the different transport formats) correctly to the individual transport channels TrCH. Even if a mobile radio device is, for example, only “interested” in the data from one of eight transport channels TrCH, it must know the transport formats of all eight transport channels TrCH.
According to the prior art, transport format combination indicator TFCI values are determined and sent in a user-specific manner.
A mobile radio device, which only belongs to one multicast group and accordingly receives data via only one transport channel TrCH, would have to know the TFS of a total of 8 transport channels TrCH instead of just that of one transport channel TrCH if, for example, a total of 8 transport channels were mapped onto the CCTrCH.
This method might be simple to implement but it has the major disadvantage, on the one hand, that an unnecessarily large storage capacity is required in the mobile radio device and, on the other hand, that it increases the signaling processing outlay in the mobile radio device.
The present invention is, therefore, directed toward sending and receiving multicast messages in a mobile radio network, particularly a so-called third generation network, in a manner that is simple and economical as far as resources are concerned.